Reflective mask blank and reflective mask

ABSTRACT

A reflective mask blank includes, on/above a substrate in the following order from the substrate side a multilayer reflective film which reflects EUV light and an absorber film which absorbs EUV light. The absorber film is a tantalum-based material film containing a tantalum-based material. The absorber film provides a peak derived from the tantalum-based material in an X-ray diffraction pattern, the peak having a peak diffraction angle (2θ) of 36.8 degrees or more and a full width at half maximum of 1.5 degrees or more.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/056,786, filed on Aug. 7, 2018, which claims foreign priority toJapanese Patent Application No. 2017-182146, filed on Sep. 22, 2017, andJapanese Patent Application No. 2017-155403, filed on Aug. 10, 2017, theentire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a reflective mask blank to be used insemiconductor manufacturing or the like, and a reflective mask obtainedby forming a pattern in an absorber film of the reflective mask blank.

Background Art

In semiconductor industry, a photolithography method using visible lightor ultraviolet light has been used as a fine pattern transfer techniquenecessary for forming an integrated circuit including a fine pattern ona Si substrate or the like. However, fining of semiconductor devices isaccelerating, but a limit of a conventional photolithography method hasbeen approached. In the photolithography method, a resolution limit of apattern is about ½ of an exposure wavelength, and it has been said thatthe resolution limit of the pattern is about ¼ of the exposurewavelength even when an immersion method is used, and the limit isexpected to be about 45 nm even when an immersion method with ArF laser(193 nm) is used. Therefore, EUV (Extreme Ultra Violet) lithographywhich is an exposure technique using EUV light of a wavelength shorterthan ArF laser is promising as an exposure technique of 45 nm orshorter. In the specification, the EUV light refers to light of awavelength in a sort X-ray region or a vacuum ultraviolet region, andspecifically refers to light of a wavelength of about 10 nm to 20 nm,particularly about 13.5 nm±0.3 nm.

Since the EUV light is easy to be absorbed by many substances and arefractive index of the substance at this wavelength is close to 1, arefractive optical system such as photolithography using conventionalvisible light or ultraviolet light cannot be used. Therefore, in EUVoptical lithography, a reflective optical system, that is, a reflectivephotomask and a mirror are used.

A reflective mask blank is a laminated body before patterning, which isused for manufacturing a reflective photomask, and has a structure inwhich a reflective layer which reflects EUV light and an absorber filmwhich absorbs EUV light are sequentially formed on/above a substratesuch as glass.

A multilayer reflective film in which a low-refractive-index layer witha low refractive index to the EUV light and a high-refractive-indexlayer with a high refractive index to the EUV light are alternatelylaminated so as to increase light reflectance when a layer surface isirradiated with the EUV light, is usually used as the reflective layer.A molybdenum (Mo) layer is usually used as tire low-refractive-indexlayer of the multilayer reflective film, and a silicon (Si) layer isusually used as the high-refractive-index layer.

A material with a high absorption coefficient to the EUV light,specifically, for example, a material containing tantalum (Ta) as a maincomponent is used in the absorber film (see Patent Literatures 1 to 5).

-   Patent Literature 1: Japanese Patent No. 5507876-   Patent Literature 2: JP-A-2012-33715-   Patent Literature 3: JP-A-2015-84447-   Patent Literature 4: JP-A-2010-206156-   Patent Literature 5: Japanese Patent No. 3806702

SUMMARY OF THE INVENTION

When manufacturing the reflective photomask from the mask blank, adesired pattern is formed in the absorber film, of the mask blank. Whenforming the pattern in the absorber film, an etching process, usually adry etching process, is used. It is preferable to have a sufficientetching rate during the dry etching process, which can improve etchingselectivity during pattern formation. When the etching selectivity isimproved, time required for patterning is shortened, productivity isimproved, and damage to the multilayer reflective film by the etchingprocess is reduced.

An object of the present invention is to provide a reflective mask blankincluding an absorber film having a sufficient etching rate dining dryetching process, and a reflective mask.

As a result of intensive studies to achieve the above object the presentinventors have found that in a case where a crystalline state of anabsorber film containing Ta and nitrogen (N) was kept in a specificstate, a sufficient etching rate can be achieved during the dry etchingprocess.

The present invention has been made based on the above findings, andprovides a reflective mask blank including, on/above a substrate in thefollowing order from the substrate side; a multilayer reflective filmwhich reflects EUV light and an absorber film which absorbs EUV light,wherein the absorber film is a tantalum-based material film containing atantalum-based material, and

wherein the absorber film provides a peak derived from a tantalum-basedmaterial in an X-ray diffraction pattern, the peak having a peakdiffraction angle 2θ of 36.8 degrees or more and a full width at halfmaximum of 1.5 degrees or more.

In the reflective mask blank, the tantalum-based material filmpreferably contains 10.0 at % to 35.0 at % of nitrogen atoms.

In the reflective mask blank, the tantalum-based material filmpreferably contains 0.05 at % or more of Krypton atoms.

It is preferred that the reflective mask blank includes a protectivefilm on the multilayer reflective film, wherein etching selectivitybetween the absorber film and the protective film is 45 or more in a dryetching process with a chlorine gas.

In the reflective mask blank, the protective film is preferably aruthenium-based material film containing a ruthenium-based material.

Further, the present invention provides a reflective mask obtained byforming a pattern in the absorber film of the reflective mask blank.

Since the reflective mask blank includes the absorber film capable ofhaving a sufficient etching rate during the dry etching process, theetching selectivity during the pattern formation is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a reflective mask blank inone embodiment of the present invention.

FIG. 2 is a graph showing X-ray diffraction patterns of Samples 1 to 4and Samples 6 and 7.

FIG. 3 shows a TEM observation result of Sample 7.

FIG. 4 shows a TEM observation result of Sample 4.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a reflective mask blank of the present invention will bedescribed with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a reflective mask blank inone embodiment of the present invention. In a reflective mask blank 1shown in FIG. 1, a multilayer reflective film 12 which reflects EUVlight and an absorber film 14 which absorbs EUV light are formedon/above a substrate 11 in this order. A protective film 13 forprotecting the multilayer reflective film 12 during pattern formation onthe absorber film 14 is formed between the multilayer reflective film 12and the absorber film 14. A backside conductive film 15 is formed on aback surface side of the substrate 11, that is, a surface side oppositeto a surface on/above which the multilayer reflective film 12, theprotective film 13, and the absorber film 14 are formed.

Hereinafter, each constituent element of the mask blank is described.

In the reflective mask blank, in the constituent shown hi FIG. 1, onlythe substrate 11, the multilayer reflective film 12 and the absorberfilm 14 are essential elements, and the protective film 13 and thebackside conductive film 15 are optional elements.

Hereinafter, each constituent element of the reflective mask blank 1 isdescribed.

The substrate 11 is required to satisfy properties as a substrate tor areflective mask blank. Therefore, it is preferable that the substrate 11has a low coefficient of thermal expansion (specifically, thecoefficient of thermal expansion at 20° C. is preferably 0±0.05×10⁻⁷/°C., particularly preferably 0±0.03×10⁻⁷/° C.), and has excellentsmoothness, flatness, and resistance to a cleaning solution used forwashing the mask blank or photomask after pattern formation.Specifically, glass having a low coefficient of thermal expansion, forexample, SiO₂—TiO₂ based glass or the like is used as the substrate 11,but the present invention is not limited thereto, and crystallized glasshaving precipitated β-quartz solid solution, quartz glass, silicon ormetal can be used.

It is preferable that the substrate 11 has a smooth surface with asurface roughness (ms) of 0.15 nm or less and flatness of 109 nm orless, since high reflectance and high transfer accuracy in thereflective photomask after pattern formation can be obtained.

A size, thickness, or the like of the substrate 11 are determinedappropriately depending on design values of a mask or the like. InExample to be described later, SiO₂—TiO₂ based glass with a 6 inches(152 mm) square in outer dimensions and a thickness of 0.25 inch (6.3mm) was used.

It is preferable to have no defect on a surface of the substrate 11 onthe side where the multilayer reflective film 12 is formed. However,even in a case where there are defects, in order to prevent occurrenceof a phase defect due to a concave defect and/or a convex defect, it ispreferable that a depth of the concave defect and a height of the convexdefect are 2 nm or less, and a full width at half maximum of the concavedefect and convex defect is 60 nm or less.

The multilayer reflective film 12 can have a high EUV light reflectanceby laminating alternately a high-refractive-index layer and alow-refractive-index layer for a plurality of times. In the multilayerreflective film 12, Mo is widely used in the low-refractive-index layer,and Si is widely used in the high-refractive-index layer. That is, aMo/Si multilayer reflective film is tire most commonly used. However,the multilayer reflective film is not limited thereto, and a Ru/Simultilayer reflective film, a Mo/Be multilayer reflective film, a Mocompound/Si compound multilayer reflective film, a Si/Mo/Ru multilayerreflective film, a Si/Mo/Ru/Mo multilayer reflective film and aSi/Ru/Mo/Ru multilayer reflective film can also be used.

The multilayer reflective film 12 is not particularly limited as long asit has desired properties a s the multilayer reflective film of thereflective mask blank. Here, the properties particularly required forthe multilayer reflective film 12 is high EUV light reflectance.Specifically, when a surface of the multilayer reflective film 12 isirradiated with light in a wavelength region of the EUV light at anincident angle of 6 degrees, a maximum value of the light reflectancearound a wavelength of 13.5 nm is preferably 60% or more, and morepreferably 65% or more. Further, even in a case where the protectivefilm 13 is placed on the multilayer reflective film 12, a maximum valueof the light reflectance around a wavelength of 13.5 nm is preferably60% or more, and more preferably 65% or more.

A film thickness of each layer constituting the multilayer reflectivefilm 12 and a number of repeating units of the layer can beappropriately selected depending on a film material to be used and theEUV light reflectance required for the multilayer reflective film.Taking a Mo/Si reflective film as an example, in order to obtain thereflective layer 12 with tire maximum EUV light reflectance of 60% ormore, the multilayer reflective film may be formed by laminating a Molayer with a film thickness of 2.3±0.1 nm and a Si layer with a filmthickness of 4.5±0.1 nm and satisfying the number of repeating units of30 to 60.

Each layer constituting the multilayer reflective film 12 may be formedto have a desired thickness by use of known deposition methods such as amagnetron sputtering method and an ion beam sputtering method. Forexample, in a case of forming a. Si/Mo multilayer reflective film by useof an ion beam sputtering method, it is preferable that a Si film isformed to have a thickness of 4.5 nm by using a Si target as a target,and using Ar gas as sputtering gas (gas pressure: 1.3*10⁻² Pa to2.7×10⁻² Pa) at an ion acceleration voltage of 300 V to 1500 V and adeposition rate of 1.8 nm/min to 18 nm/min; and then, a Mo film isformed to have a thickness of 2.3 nm by using a Mo target as a target,and using Ar gas as sputtering gas (gas pressure: 1.3×10⁻² Pa to2.7×10⁻² Pa) at an ion acceleration voltage of 300 V to 1500 V and adeposition rate of 1.8 nm/min to 18 nm/min. When the above formationprocedure is taken as one cycle, the Si/Mo multilayer reflective film isformed by laminating the Si film, anti the Mo film in 40 to 50 cycles.

In order to prevent a surface of the multilayer reflective film 12 frombeing oxidized, it is preferable that the uppermost layer of themultilayer reflective film 12 is a layer of a material which isdifficult to be oxidized. The layer of a material which is difficult tobe oxidized functions as a cap layer of the multilayer reflective film12. A Si layer is exemplified as a specific example of the layer whichfunctions as the cap layer and is formed of a material difficult to beoxidized. In a case where the multilayer reflective film 12 is a Si/Mofilm, the uppermost layer can function as a cap layer by using a Silayer as the uppermost layer. In that case, it is preferable that a filmthickness of the cap layer is 11±2 nm.

The protective film 13 is an optional constituent element that isprovided for a purpose of protecting the multilayer reflective film 12such that the multilayer reflective film 12 is not damaged by an etchingprocess when the absorber film 14 is patterned by the etching process,usually a dry etching process. However, from the view point ofprotecting the multilayer reflective film 12, it is preferable to formthe protective film 13 on the multilayer reflective film 12.

A substance which is difficult to be affected by the etching process forthe absorber film 14, that is, a substance in which an etching ratethereof is smaller than that of the absorber film 14 and which isdifficult to be damaged by the etching process, is selected as amaterial of the protective film 13.

Further, in order not to impair the EUV reflectance in the multilayerreflective film 12 even after the protective film 13 is formed, it ispreferable to select a substance with a high EUV reflectance as theprotective film 13.

It is preferable that the protective film 13 is a ruthenium-basedmaterial film containing a ruthenium-based material. In thespecification, the term of “ruthenium-based material” refers to Ru andRu compounds (e.g., RuB, RuSi, etc.). An amount of Ru in theruthenium-based material film is preferably 50 at % or more, morepreferably 70 at % or more, still more preferably 90 at % or more, andparticularly preferably 95 at % or more.

In a case of forming the protective film 13 on the multilayer reflectivefilm 12, it is preferable that a thickness of the protective film 13 is1 nm to 10 nm for reasons of increasing the EUV reflectance andobtaining the satisfactory etching resistance. The thickness of theprotective film 13 is preferably 1 nm to 5 nm, and more preferably 2 nmto 4 nm.

In a case of framing the protective film 13 on the multilayer reflectivefilm 12, the protective film 13 can be formed by known depositionmethods such as a magnetron sputtering method and an ion beam sputteringmethod.

In a case of using an ion beam sputtering method to form a Ru film asthe protective film 13, a Ru target may be used as a target and may bedischarged under an argon (Ar) atmosphere. Specifically, the ion beamsputtering may be performed under the following conditions:

Sputtering Gas: Ar (gas pressure: 1.3×10⁻² Pa to 2.7×10⁻² Pa)

Ion Acceleration Voltage: 300 V to 1500 V

Deposition Rate: 1.8 nm/min to 18.0 nm/min

As the property particularly required for the absorber film 14,extremely low EUV reflectance thereof is exemplified. Specifically, whena surface of the absorber film 14 is irradiated with light in awavelength region of the EUV light, a maximum light reflectance around awavelength of 13.5 nm is preferably 2.0% or less, more preferably 1.0%or less, still more preferably 0.5% or less, and particularly preferably0.1% or less.

In order to achieve the above properties, the absorber film 14 is formedof a material with a high absorption coefficient of EUV light. In thereflective mask blank 1, a tantalum-based material film containing atantalum-based material is used as a material which has a highabsorption coefficient of EUV light mid is used for forming the absorberfilm 14. The reason why the tantalum-based material film is used is thatthe material is chemically stable, the material is easy to be etchedduring pattern formation of the absorber film, and the like. In thespecification, the term of “tantalum-based material” refers to tantalum(Ta) and Ta compounds.

It is preferable that the tantalum-based material film contains Ta andnitrogen (N), since crystallization of Ta can be prevented and thecrystal can be prevented from becoming larger and increasing the surfaceroughness.

In a case where the tantalum-based material film contains Ta and N, inorder to achieve the later-described conditions in an X-ray diffractionpattern of the absorber film 14 and to increase the etching selectivity,an amount of N atoms is preferably 10.0 at % to 35.0 at %, morepreferably 10.0 at % to 25.0 at %, still more preferably 10.5 at % to18.0 at %, and particularly preferably 11.0 at % to 16.0 at %.

In a case where the tantalum-based material film contains Ta and N, thetantalum-based material film may further contain at least one elementselected from hafnium (Hf), silicon (Si), zirconium (Zr), titanium (Ti),germanium (Ge), boron (B), tin (Sn), nickel (Ni), cobalt (Co) andhydrogen (H). In a case of containing these elements, a total contentratio thereof in the tantalum-based material film is preferably 10 at %or less,

The absorber film 14 which is a tantalum-based material film has a peakderived from the tantalum-based material in the X-ray diffractionpattern. In the reflective mask blank 1, when the peak derived from thetantalum-based material satisfies the Conditions 1 and 2 shown below,the etching rate is sufficient during the dry etching process.

Condition 1: A peak diffraction angle 2θ of the peak is 36.8 degrees ormore

Condition 2: A full width at half maximum of the peak is 1.5 degrees orless

In the specification, the full width a t half maximum is also referredto as FWHM.

In a case where the peak diffraction angle 2θ of the peak is less than36.8 degrees, a ratio of amorphous phase in a crystalline phaseincreases and the etching rate during the dry etching process decreases.Meanwhile, when the peak diffraction angle 2θ is 36.8 degrees or more, amixed phase state of an amorphous phase and a microcrystalline phase ina crystalline phase becomes appropriate and etching proceeds easily at aphase interface, so that the etching rate increases.

The peak diffraction angle 2θ of the peak is preferably in a range of36.8 degrees to 40.0 degrees, and more preferably hi a range of 37.0degrees to 39.0 degrees.

In a case where the full width at half maximum of the peak Is less than1.5 degrees, crystallinity of the tantalum-based material filmincreases, so that coarse crystal grains are formed on a surface of thetantalum-based material film. The coarse crystal grains on the surfaceof the tantalum-based material film may be detected as adhered foreignmatters during defect inspection, it becomes difficult to distinguishthe coarse crystal grains from adhered foreign matters which should beoriginally inspected, and accuracy of defect inspection may be lowered.Rather, it may be difficult to uniformly etch the absorber film and thesurface roughness after etching may be rough.

The full width at half maximum of the peak is preferably 2.5 degrees to6 degrees, and more preferably 3.0 degrees to 5.0 degrees.

The absorber film 14 satisfying the Conditions 1 and 2 described abovehas a sufficient etching rate during the dry etching process, and theetching selectivity between the absorber film and the multilayerreflective film, (in a case where no protective film is formed on themultilayer reflective film) or the protective film (in a case where theprotective film is formed on the multilayer reflective film) increases.For example, an etching rate during the dry etching process usingchlorine-based gas as etching gas is fast, and etching selectivitybetween the absorber film and the protective film 13 is 45 or more. Inthe specification, the etching selectivity can be calculated using, forexample, the following formula.

Etching Selectivity=(Etching Rate of Absorber Film 14)/(Etching Rate ofProtective Film 13)

The etching selectivity during the dry etching process using thechlorine-based gas as the etching gas is preferably 45 or more, morepreferably 50 or more, still more preferably 55 or more, andparticularly preferably 60 or more. In addition, the etching selectivityis preferably 250 or less, and more preferably 190 or less.

A film thickness of the absorber film 14 is preferably 5 nm or more,more preferably 20 nm or more, still more preferably 30 nm or more, andparticularly preferably 35 nm or more.

Meanwhile, when the film thickness of the absorber film 14 is too large,accuracy of a pattern to be formed in the absorber film 14 may decrease,so that the film thickness is preferably 100 nm or less, more preferably99 nm or less, and still more preferably 80 nm or less.

The film thickness of the absorber film 14 can be reduced by use of aprinciple of phase shift or by including elements with a high absorptioncoefficient (e.g. Sn, Ni, Co. or the like) in the absorber film 14.

The absorber film 14 can be formed by known deposition methods such assputtering methods, for example, the magnetron sputtering method raidthe ion beam sputtering method.

In a case of forming a TaN layer as the absorber film 14, when themagnetron sputtering method is used, a TaN layer can be formed by usinga Ta target mid discharging the target under a nitrogen (N₂) atmospherediluted with Ar.

In order to form the TaN layer as the absorber film 14 by the methoddescribed above, specifically, the method may be performed under thefollowing deposition conditions.

Sputtering Gas: mixed gas of rare gas and N₂ (N₂ gas concentration: 3vol % to 80 vol %, preferably 5 vol % to 30 vol %, and more preferably 8vol % to 15 vol %; gas pressure: 0.5×10⁻¹ Pa to 10×10⁻¹ Pa, preferably0.5×10⁻¹ Pa to 5×10⁻¹ Pa, and more preferably 0.5×10⁻¹ Pa to 3×10⁻¹ Pa).

Input Power (for each target): 30 W to 2000 W, preferably 50 W to 1500W, and more preferably 80 W to 1000 W.

Deposition Rate: 2.0 nm/min to 60 nm/min, preferably 3.5 nm/min to 45nm/min, and more preferably 5 nm/min to 30 nm/min.

It is preferable to use krypton (Kr) as the rare gas in the sputteringgas, since film distortion during formation of the absorber film 14 canbe prevented and deformation, of the substrate can be avoided.

The absorber film 14 formed by using krypton (Kr) as tire rare gas inthe sputtering gas contains 0.05 at % or more of Kr atoms. The upperlimit of krypton (Kr) atoms is preferably 1%, and more preferably 0.3%.

Electrical conductivity and a thickness of a constituent material areselected for the backside conductive film 15, so as to make sheetresistance thereof to be 100 Ω/square or less. The constituent materialof the backside conductive film 15 can be widely selected from thosedescribed in known documents. For example, examples of the constituentmaterial include high dielectric constant material layers described inJP-A-2003-501823 and WO-A1-2008/072706, specifically, a material layerselected from the group consisting of silicon, TiN, molybdenum, chromium(Cr), CrN, and TaSi. The backside conductive film can be formed by,specifically, for example, sputtering methods such as the magnetronsputtering method and the ion beam sputtering method, and dry depositionmethods such as a CVD method and a vacuum vapor deposition method. Forexample, in a case where a CrN film is formed by the magnetronsputtering method, the magnetron sputtering may be performed by settinga target to be a Cr target and setting a sputtering gas to be a mixedgas of Ar and N₂. Specifically, the method may be performed under thefollowing deposition conditions.

Target: Cr target

Sputtering Gas: mixed gas of Ar and N₂ (N₂ gas concentration: 10 vol %to 80 vol %, and gas pressure: 0.02 Pa to 5 Pa).

Input Power: 30 W to 2000 W

Deposition Rate: 2.0 nm/min to 60 nm/min

The reflective mask blank may have other constituent elements excludingthose described above. For example, a low reflective layer or a hardmask may be formed for inspection light which is used for inspecting amask pattern on/above the absorber film.

Examples of the low reflective layer include materials containing atleast one element of Ta, Hf, Si, Zr, Ti, Ge, B, Sn, Ni, Co, N, H, and O,for example, TaO, TaON, TaONH, TaHfO, TaHfON, or the like.

Examples of the material of the hard mask layer include materialscontaining at least one element of Cr, Ru, Zr, In, Si, N, H, and O, forexample, CrN, CrON, Ru, SiO₂, SiON, Si₃N₄, SiC, or the like

Examples

The present invention is described below along Examples.

Cases 1 to 5 are working examples, and Cases 6 and 7 are comparativeexamples.

(Case 1)

The reflective mask blank was manufactured by the following method.

First, a glass substrate (SiO₂—TiO₂-based glass substrate) with a lengthof 152.4 nm, a width of 152.4 mm, and a thickness of 6.3 mm was preparedas the substrate.

The glass substrate has a coefficient of thermal expansion of 0.2×10⁻⁷/°C., a Young's modulus of 67 GPa, a Poisson's ratio of 0.17, and aspecific rigidity of 3.07×10⁷ m²/s². The glass substrate was polishedsuch that a main surface thereof has a surface roughness (root meansquare height Sq) of 0.15 nm or less and flatness of 100 nm or less.

Next, a backside conductive film was formed on one surface (a secondmain surface) of the glass substrate. The backside conductive film was aCrN film and was formed to have a thickness of about 100 nm by themagnetron sputtering method. Sheet resistance of the backside conductivefilm is 100 Ω/square.

Next, an electrostatic chuck was used to fix the glass substrate in adeposition chamber in an electrostatic adsorption way via the backsideconductive film. In this state, a multilayer reflective film was teamedon a first main surface of the glass substrate.

In the deposition, a Mo/Si multilayer reflective film was formed by useof the ion beam sputtering method to alternately form an Mo layer with athickness of 2.3 nm and an Si layer with a thickness of 4.5 nm for 50times.

In the deposition of the Mo layer, the ion beam sputtering was performedusing a Mo target under an Ar gas atmosphere (gas pressure: 0.02 Pa). Anapplied voltage was set to 700 V, and a deposition rate was set to 3.84nm/min.

Meanwhile, in the deposition of the Si layer, the ion beam sputteringwas performed using a boron-doped Si target under an Ar gas atmosphere(gas pressure: 0.02 Pa). Air applied voltage was set to 700 V, and adeposition rate was set to 4.62 nm/min.

A total thickness (target value) of the multilayer reflective film is(2.3 nm+4.5 nm)×50 times=340 nm. The uppermost layer of the multilayerreflective film was a Si layer.

Next, a protective film, was formed on the multilayer reflective film bythe ion beam sputtering method.

The protective film was a Ru layer, and the ion beam sputtering wasperformed using a Ru target under an Ar gas atmosphere (gas pressure:0.02 Pa). An applied voltage was set to 700 V, and a deposition rate wasset to 3.12 nm/min. A film thickness of the protective film was set to2.5 nm.

Next, an absorber film was formed on the protective film by themagnetron sputtering method.

The absorber film was a TaN layer, and the magnetron sputtering wasperformed using a Ta target under an atmosphere of a mixed gas of Kr andN₂ (Kr=95 vol % and N₂=5 vol %). A deposition rate was set to 7.7nm/min, and a film thickness was set to 75 nm.

Accordingly, Sample 1 tor evaluating properties of the absorber film ofthe reflective mask blank in Case 1 was obtained.

Next, a low reflective layer was formed on the absorber film by themagnetron sputtering method.

The low reflective layer was a TaON layer, and the magnetron sputteringwas performed, using a Ta target, under an atmosphere of a mixed gas ofAr, O₂ and N₂ (Ar=60 vol %, O₂=30 vol %, and N₂=10 vol %). A depositionrate was set to 1.32 nm/min. A film thickness of the low reflectivelayer was set to 5 nm.

Accordingly, the reflective mask blank in Case 1 was manufactured.

(Case 2)

The reflective mask blank was manufactured by the same method as that ofCase 1.

However, in this Case 2, the conditions for forming the TaN layer as theabsorber film by the magnetron sputtering method was changed from thoseof Case 1. More specifically, a mixing ratio (volume ratio) of Kr and N₂in the mixed gas was set to 93:7. The other conditions are the same asthose of Case 1.

As with Case 1, a sample for evaluating the properties of the absorberfilm of the reflective mask blank including the formed absorber film wasobtained. The sample is referred to as “Sample 2” (the same applieshereinafter).

(Case 3)

The reflective mask blank, was manufactured by the same method as thatof Case 1.

However, in this Case 3, the conditions for forming the TaN layer as theabsorber film by the magnetron sputtering method was changed from thoseof Case 1. More specifically, a mixing ratio (volume ratio) of Kr and N₂in the mixed gas was set to 91:9. The other conditions are the sane asthose of Case 1.

(Case 4)

The reflective mask blank was manufactured by the same method as that ofCase 1.

However, in this Case 4, the conditions for forming the TaN layer as theabsorber film by the magnetron sputtering method was changed from thoseof Case 1. More specifically, a mixing ratio (volume ratio) of Kr and N₂in the mixed gas was set to 89:11. The other conditions are the sane asthose of Case 1.

(Case 5)

The reflective mask blank was manufactured by the same method as that ofCase 1.

However, in this Case 5, the conditions for forming the TaN layer as theabsorber film by the magnetron sputtering method was changed from thoseof Case 1. More specifically, a mixed gas of Ar, Kr and N₂ was used asthe mixed gas. A mixing ratio (volume ratio) of Ar, Kr and N₂ was set to54:38:8. The other conditions are the same as those of Case 1.

(Case 6)

The reflective mask blank was manufactured by the same method as that ofCase 1.

However, in this Case 6, the conditions for forming the TaN layer as theabsorber film by the magnetron sputtering method, was changed from thoseof Case 1. More specifically, a mixed gas of Ar, Kr and N₂ was used asthe mixed gas. A mixing ratio (Volume ratio) of Ar, Kr and N₂ was set to67:17:16. The other conditions are the same as those of Case 1.

(Case 7)

The reflective mask blank was manufactured by the same method as that ofCase 1.

However, in this Case 7, the conditions for forming the TaN layer as theabsorber film by the magnetron sputtering method was changed for thoseof Case 1. More specifically, a mixing ratio (volume ratio) of Kr and N₂in the mixed gas was set to 94:6. The other conditions are the same asthose of Case 1.

(Evaluation)

The following evaluations were made by use of each sample manufacturedas described above.

(XRD Measurement)

An X-ray diffraction device (model: ATX-G, manufacturer: RigakuCorporation) was used to perform XRD measurement using an in-planemethod. In the measurement, a position where a width limit slit of 1 mmand a vertical limit slit of 10 mm were overlapped and a position wherea width limit slit of 0.1 mm and a vertical limit slit, of 10 mm wereoverlapped was arranged at two positions from an incident side ofX-rays, and a solar slit with a divergence angle of 0.48 degree wasarranged therebetween. A solar slit with a divergence angle of 0.41degree was arranged on a light receiving side. The measurement wasperformed using Cu—Kα rays (wavelength: 1.5418 Å) at an output of 50 kVand 300 mA as an X-ray source under the conditions of an incident angleof 0.6 degree, a step width of 0.05 degree, and a scanning speed of 1degree/min, thereby obtaining data.

X-ray analysis software (model: PDXL2, manufacturer: Rigaku Corporation)was used for analysis of the measurement data. Data process of B-Splinesmoothing (X threshold: 1.50), background removal (a fitting method),Kα2 removal (intensity ratio: 0.497), peak search (second derivativemethod, σ cut value: 3.00), and profile fitting (fitting to measureddata, peak shape: split type Voigt function) was performed to obtain thediffraction angle 2θ mid the full width at half maximum.

FIG. 2 is a graph showing X-ray diffraction patterns of Samples 1 to 4and Samples 6 and 7. In FIG. 2, a fixed value is added to an intensity(eps) value of the X-ray diffraction peak of each sample to shift theintensity of the X-ray diffraction peak of each sample, so that it iseasy to observe a peak shape. Therefore, a scale on a vertical axis isnot an absolute value of the intensity but mere intensity (cps).

(Etching Rate Evaluation)

Reactive ion etching was performed using an etching device (model:CE-300R, manufacturer: ULVAC Inc.) under an atmosphere of a mixed gas ofCl₂ and He (Cl₂=20 vol %, He=80 vol %). Then, film thicknesses (nm) ofthe absorber film and the protective film after etching were measuredusing an X-ray reflectance measuring device (model: SmartLab HTP,manufacturer: Rigaku Corporation), thereby obtaining the etching rates(nm/min) of the absorber film and the protective film. The etchingselectivity was obtained, from the etching rate of the absorber filmwith respect to the etching rate of the protective film (etching rate ofabsorber film/etching rate of protective film). The etching rate of theprotective film is 0.047 nm/sec in each case.

(Film Composition Evaluation)

An amount of Ta (at %), an amount of N (at %) and an amount of Kr (at %)in the absorber films of Samples 1 to 7 were obtained using a Rutherfordbackscattering analyzing device (model: RBS, manufacturer: KobelcoResearch Institute). Further, since values of the amounts of N in thefilms of Samples 1 to 3 and 7 were small, the amount could not bequantitatively evaluated with high accuracy by the Rutherfordbackscattering analyzing device. Therefore, the amount of Ta (at %) andthe amount of N (at %) were measured using an electron beanmicroanalyzer (model: JXA-8500F, manufacturer: JEOL Ltd.). In themeasurement by the electron beam microanalyzer, an acceleration voltagewas set to 4 kV, an irradiation current was set to 30 nA, and a beamdiameter was set to 100 μm, and Kα ray was measured for N by using LDE1Has an analyzing crystal of N, and Mα ray was measured for Ta by usingPETJ as an analyzing crystal of Ta. The amount of Ta. (at %) and theamount of N (at %) were quantified by a calibration curve method,standardized to be 100 wt % with Ta and N, and then were converted intoat %. As a standard sample, Sample 4 in which, the amount of N (at %)was determined by Rutherford backscattering analysis and a Ta filmcontaining no N were used.

(Defect Inspection)

Defect inspection was performed on each sample in the followingprocedures.

A defect inspection device using visible light laser (model: M1350,manufacturer: Lasertec) was used to perform, the defect inspection on asurface on an absorption layer side of each sample. An evaluation regionwas set to a range of 132 mm×132 mm.

In Sample 7, in the inspection with the defect inspection device, 500 ormore defects of 100 nm or less was detected, but when the surface wasobserved with a scanning electron microscope (model: Ultra 60,manufacturer: Carl Zeiss), there were no defects actually, and no realdefects were confirmed. For this reason, those detected as the defectsof 100 nm or less by the detect inspection device were found to be falsedefects due to the surface roughness. Presence of such false detectshinders accurate evaluation of real defects.

Inspectability of samples, in which many false defects were detected andaccurate defect inspection was difficult, was determined as B.Meanwhile, inspectability of samples, for which the accurate defectinspection can be can performed, was determined as A.

Sample 4 and Sample 7 were observed by TEM in the following procedures.

A sample for TEM (hereinafter also referred to as a transmissionelectron microscope) observation was obtained by polishing the substrateside on which the absorber film was formed and preparing a thin sampleof only the absorber film. A mechanical polishing machine (model: BetaGrinder Polisher, manufacturer: Burea) and an ion polishing machine(model: Precision Ion Polishing System Model 691, manufacturer: Gatan)were used for the polishing of the substrate side. The thin sample ofonly the absorber film was observed from, a planar direction of theabsorber film using a transmission electron microscope (model:JEM-2010F, manufacturer: JEOL Ltd.) at an acceleration voltage of 200kV. FIG. 3 shows a TEM observation result of Sample 7, and FIG. 4 showsa TEM observation result of Sample 4. It can be seen that a surface ofSample 7 is remarkably rough.

Further, under the same conditions as those of Example 1, samples havingfilm thicknesses of 50 nm and 58 nm were manufactured and evaluated,respectively. As a result the performance was the same as that of Sample1.

The results are shown in the following table.

TABLE 1 Deposition gas flow (vol %) Film thickness of Ar Kr N₂ absorberfilm (nm) Sample 1  0% 95%  5% 75 Sample 2  0% 93%  7% 76 Sample 3  0%91%  9% 76 Sample 4  0% 89% 11% 76 Sample 5 54% 38%  8% 75 Sample 6 67%17% 16% 76 Sample 7  0% 94%  6% 77

TABLE 2 Full width at Diffraction N in absorber Kr in absorber EtchingRate of half maximum angle film film Absorber film Etching Inspect-(deg) (deg) (at %) (at %) (nm/sec) Selectivity ability Sample 1 3.5 37.211.7 0.07 3.50 75.10 A Sample 2 4.2 37.1 14.6 0.07 3.19 68.40 A Sample 34.6 37.2 16.8 0.07 2.74 58.74 A Sample 4 4.5 37.1 18.3 0.07 2.32 49.62 ASample 5 4.4 37.1 21.9 0.07 2.25 48.28 A Sample 6 4.4 36.6 39.4 0.101.25 26.82 A Sample 7 1.3 37.8 9.5 0.10 2.77 59.28 B

In any of Samples 1 to 5, the etching rate daring the dry etchingprocess of the absorber film with chlorine gas was high and the etchingselectivity between the absorber film and the protective film was high.In contrast, in Sample 6 with a diffraction angle 2θ of less than 36.8degrees, the etching rate during the dry etching process of the absorberfilm with chlorine gas was small and the etching selectivity between theabsorber film and the protective film was low. Meanwhile, in Sample 7with a foil width at half maximum, of less than 1.5 degrees, as shown inFIG. 3, coarse crystal grains were formed on a surface of the absorberfilm. Farther, the evaluation result of inspectability for Sample 7 wasdetermined as B. In any one of Samples 1 to 7, a value of the EUVreflectance around 13.5 nm was 1.5% or less, and the EUV absorptionproperties required for the absorber film were satisfied.

While the present invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing horn the spirit and scope thereof.

This application is based on Japanese Patent Application No. 2017-155403filed on Aug. 10, 2017 and Japanese Patent Application No. 2017-182146filed on Sep. 22, 2017, the entire subject matters of which areincorporated herein by reference.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 EUV mask blank    -   11 Substrate    -   12 Reflective layer (multilayer reflective film)    -   13 Protective film    -   14 Absorber film    -   15 Backside conductive film

1. A reflective mask blank comprising, on/above a substrate in thefollowing order from the substrate side: a multilayer reflective filmwhich reflects EUV light; and an absorber film which absorbs EUV light,wherein the absorber film is a tantalum-based material film comprising atantalum-based material, wherein the tantalum-based material filmcomprises 10.0 at % to 25.0 at % of nitrogen atoms, wherein the absorberfilm provides a peak derived from the tantalum-based material in anX-ray diffraction pattern, the peak having a peak diffraction angle (2θ)of 36.8 degrees to 40.0 degrees and a fell width at half maximum of 1.5degrees to 6.0 degrees, and wherein etching selectivity between theabsorber film and the protective film is 45 or more in a dry etchingprocess with a chlorine gas.
 2. The reflective mask blank according toclaim 1, wherein the tantalum-based material film comprises 18.0 at % to25.0 at % of nitrogen atoms.
 3. The reflective mask blank according toclaim 1, wherein the tantalum-based material film contains 0.05 at % ormore of Krypton atoms.
 4. The reflective mask blank according to claim1, wherein the protective film is a ruthenium-based material filmcontaining a ruthenium-based material.
 5. A reflective mask obtained byforming a pattern in the absorber film of the reflective mask blankaccording to claim 1.